White LED lighting device and a lighting appliance

ABSTRACT

An LED lighting device ( 6 ) having an LED ( 8 ) emitting white light and optical filter means ( 12 ) suitable for filtering the white light emitted by the LED ( 8 ). The optical filter means comprise at least two optical filters ( 12 ) that have different transmission coefficients and that are positionable to filter the light emitted by the LED ( 8 ) individually. The lighting device ( 6 ) includes a power supply unit ( 10 ) suitable for delivering different power supply currents to the LED ( 8 ) depending on whether one or the other of the optical filters ( 12 ) is positioned to filter the light from the LED ( 8 ), so as to modify the color temperature of the light emitted by the LED ( 8 ).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC § 119 to French PatentApplication No. 12 52735 filed on Mar. 27, 2012, which application ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to a light-emitting diode (LED) lighting devicehaving an LED emitting white light and optical filter means suitable forfiltering said white light emitted by the LED.

The invention also provides a lighting appliance for an operatingtheater including such a lighting device.

PRIOR ART

More particularly, the invention applies to a lighting device intendedmainly for use in a medical situation, in particular in an operatingtheater. Such a lighting device needs to enable a surgeon to operateunder good conditions, and in particular to distinguish correctlybetween the various types of tissue. For this purpose, the lightingdevice needs to comply with certain standards and to produce light thatis generally white, presenting a color rendering index (RCI) lying inthe range 85 to 100. In addition, the color temperature of the lightproduced by the lighting device must lie in the range 3000 K (warmcolors) and 6700 K (cool colors), in accordance with the standard IEC60601-2-41, so as to enable the surgeon to distinguish small colordifferences without effort.

The term “color temperature” as applied to light is used to mean theequivalent color temperature evaluated, in well-known manner, as are thechromatic coordinates (x,y), on the basis of the spectrum of the lightin a reference chromatic diagram of the International Commission onIllumination (CIE).

A distinction is made between the light flux from a light source, whichis the light power it emits expressed in lumens, and the visualillumination provided by a lighting device in an illuminated field,which is the quantity of light flux lighting the illuminated fieldexpressed in lux, i.e. in lumens per square meter (lm/m²).

Depending on the operation to be performed, the surgeon may have a widevariety of lighting needs and those needs may even vary as the operationprogresses. That is why it is desirable for the surgeon to be able tomodify the spectral characteristics of the light produced by thelighting device, such as its color temperature or the chromaticcoordinates, so as to obtain different colors of white that areappropriate for the operation.

At present, various different types of lighting device are in existencethat satisfy the lighting requirements of medical conditions that use amixture of white LEDs and of color LEDs in order to obtain whitelighting at a desired color temperature, but none of them proposes alighting device having a modifiable spectral characteristic.

For example, patent document DE 10 2006 040393 discloses an LED lightingdevice that produces white illuminating light from LEDs emitting coolwhite light, warm white light, red light, and green light. That devicemakes use in particular of an optical filter placed directly on an LEDemitting cold white light in order to obtain warm white light. However,the color temperature and the illuminating light emitted by the lightingdevice are not modifiable. It is also known that filters reduce thelight flux of the illuminating light, which is not desirable.

Also known is patent document WO 2008/087404, which discloses a lightingdevice that produces white illuminating light from white LEDs and redLEDs. By using an optical filter placed in front of the white LEDs, thatlighting device enables a desired color temperature to be obtained forthe illuminating light. Nevertheless, that lighting device does notenable the surgeon to modify the color temperature of the illuminatinglight.

A drawback of those two prior devices lies in the fact that when anobstacle is masking a fraction of the light flux (e.g. when the surgeonleans over), then the balance between the contributions of the variouscolored LEDs is lost, thereby modifying the color temperature of thelight produced by the lighting device, producing a rainbow effect, andforming colored shadows in the illuminated field.

SUMMARY OF THE INVENTION

The object of the invention is to remedy all those drawbacks byproposing an LED lighting device that produces white illuminating lightin an illuminated field having spectral characteristics, such as forexample color temperature, that are adjustable by the surgeon withoutreducing the visible illumination in the illuminated field.

To this end, the invention provides an LED lighting device having an LEDemitting white light and optical filter means suitable for filteringsaid white light emitted by the LED, the device being characterized inthat said optical filter means comprise at least two optical filtersthat have different transmission coefficients and that are positionableto filter said light emitted by the LED individually, and in that thelighting device includes a power supply unit suitable for deliveringdifferent power supply currents to said LED depending on whether one orthe other of the optical filters is positioned to filter said light fromthe LED, so as to modify the color temperature of the light emitted bythe LED.

With such an arrangement of the lighting device of the invention, thespectral characteristics of the illumination in the illuminated field,in particular the color temperature or the chromatic coordinates andthus the white color, are easily adjustable, merely by changing theoptical filter without modifying the visual illumination in theilluminated field, since the light flux from the LED is conserved byvarying the power supply to the LED.

Another advantage of the lighting device of the invention is that byusing white LEDs only, the color temperature that is obtained is notmodified in the presence of an obstacle in the light flux.

For example, the lighting device of the invention may advantageouslyinclude at least one optical filter suitable for attenuating a redcomponent of the light emitted by the LED so as to attenuate the energydelivered by the LED, i.e. reduce its radiant energy. Such an opticalfilter, also referred to as a “cold” filter, serves to block the longestwavelengths while remaining neutral in terms of color perception by thehuman eye in the visible domain, i.e. such a filter modifies neither thecolor temperature nor the color rendering index of the light produced bythe lighting device.

With the lighting device of the invention, it is thus possible to reducethe radiant energy from the light source, which is both a source ofdrying so far as the patient is concerned and of inconvenience for themedical staff. It should be recalled that radiant energy isconventionally defined as the ratio of energy intensity expressed inwatts per square meter (W/m²) and illuminance expressed in lux. Energyintensity covers all radiation in the range 300 nanometers (nm) to 2500nm. By way of comparison, visual illuminance covers illumination in therange 360 nm to 780 nm and it is weighted by the sensitivity of the eye,which is practically zero beyond 700 nm. A “cold” optical filter asdescribed above thus enables energy intensity to be lowered withoutmodifying visual illuminance and without affecting either the colortemperature nor any other colorimetric properties.

Advantageously, the lighting device of the invention may include atleast one optical filter suitable for attenuating a blue component ofthe light emitted by the LED at a wavelength lying in the range 400 nmto 480 nm. Such an optical filter, referred to herein as a “blue”filter, serves to provide illumination of the illuminated field that isbalanced over all visible wavelengths and that provides very good colorperception for the surgeon, and limiting photobiological risks.

It is known that LEDs, and in particular white LEDs, possess in theiremission spectrum a high proportion of blue component, commonly referredto as the “blue peak”. Such unbalance in the components of the whitelight emitted by LEDs affects color perception by the surgeon. Inaddition, it is known that excess blue components, in the meaning of thestandard EN62471, increases photobiological risk. FIG. 1 shows anexample of the emission spectrum of a white LED, i.e. the relativeintensity I emitted by the LED as a function of the wavelength of thelight emitted by the LED. The example of FIG. 1 shows clearly,identified by arrow P, the presence in the emission spectrum of a bluepeak at short wavelengths lying in the range about 400 nm to 480 nm, andcentered around 450 nm.

A “blue” optical filter as defined above makes it possible to attenuatelight in a wavelength range that presents the greatest bluephotobiological risk, as defined for example in standard EN62471: 2008.In addition, such a “blue” optical filter advantageously makes itpossible to reduce the color temperature of the light produced by thelighting device, thereby providing the surgeon with the option ofvarying the color temperature of the lighting in simple and easy mannerin order to adapt it to requirements.

A lighting device of the invention may advantageously present thefollowing features:

-   -   the lighting device comprises a plurality of consecutive optical        filters having progressive transmission coefficients for        attenuating the blue component;    -   the attenuation difference between two consecutive optical        filters is at least 15%;    -   the lighting device has a plurality of identical LEDs, each        emitting white light;    -   each LED is associated with a set of optical filters having        different transmission coefficients, the sets of optical filters        being identical from one LED to another;    -   said optical filters are arranged on a rotary disk; and    -   said filters are arranged at the periphery of said rotary disk.

The invention also extends to a lighting appliance for an operatingtheater including at least one such lighting device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be better understood and other advantagesappear on reading the detailed description of an embodiment taken by wayof non-limiting example and shown in the accompanying drawings, inwhich:

FIG. 1 is a graph showing the emission spectrum of a white LED;

FIG. 2 is a diagrammatic perspective view of a lighting appliancecomprising four lighting devices of the invention;

FIG. 3 is a diagrammatic perspective view of the rear portion of one ofthe FIG. 2 lighting devices;

FIG. 4 is a diagrammatic section view on axis IV-IV in FIG. 3 showing aportion of the FIG. 2 lighting device; and

FIG. 5 shows the transmission coefficients of three optical filters of alighting device of the invention.

DESCRIPTION OF EMBODIMENTS

FIG. 2 shows a lighting appliance 1 lighting an illuminated field 2,here a field where a surgeon is operating on a patient.

The lighting appliance 1 is of the type that is suspended from theceiling of the operating theater in known manner, and it comprises ahinged suspension arm 3 carrying an overhead light 4.

As can be seen in FIG. 2, the light 4 is in the form of a cross in whicheach of its branches comprises a lighting device 6 of the inventioninserted in a housing 7 of the light 4. As an example, the lightingdevices 6 are substantially identical, each of them having foursubstantially identical lighting outlets 5.

Advantageously, the lighting devices 6 have LEDs 8 arranged to emitwhite light, and preferably each lighting outlet 5 has only one whiteLED 8. By way of example, the LED 8 emits white light with a colortemperature of 5000 K.

FIG. 3 is a diagrammatic enlarged view of a lighting device 6 of theinvention without the housing 7 in order to show its optical elementsmore clearly.

As can be seen in FIG. 3, each lighting outlet 5 thus comprises thewhite LED 8 in front of which there is arranged a conventionalcollimator 9 to direct the light flux from the LED 8 towards thelighting field 2, and interposed between the collimator 9 and the LED 8,there are optical filter means 12 for filtering the light emitted by theLED 8. A radiator 15 is preferably arranged adjacent to the LED 8 inorder to dissipate the heat produced by the LED 8.

FIG. 4 shows the lighting device 6 in cross-section on axis IV-IV ofFIG. 3 in order to show more clearly that each optical filter 12 isarranged between a LED 8 and a collimator 9, this configuration makingit possible to use optical filters 12 of small size.

Advantageously, the optical filter means comprise, for each LED 8, aplurality of optical filters 12, three optical filters 12 in thisexample, that are arranged consecutively and that have transmissioncoefficients that are different and preferably progressive, whichfilters are positioned to filter individually the light emitted by eachLED 8 so as to obtain different colors of white, i.e. so as to obtain avariable color temperature or variable chromatic coordinates.

More precisely, the lighting device 6 has a support 11 for supportingthe optical filters 12 that are mounted to pivot about an axis A in sucha manner that the optical filters 12 and the LEDs 8 are movable relativeto one another. The support 11 in this example is in the form of a disk,with the optical filters 12 being arranged at the periphery 11A of thedisk 11 and being aligned on a circle centered on the axis A, and theLEDs 8 are arranged at the four corners of a square that is inscribed inthe circle formed by the optical filters 12 such that, when the disk 11turns about the axis A, the optical filters 12 occupy successivepositions in which they are in axial alignment with the LEDs 8 so thatthe white light emitted by those LEDs 8 passes through them. It can thusreadily be understood that for each position of the disk 11 about theaxis A, each LED 8 is in axial alignment with an optical filter 12,which consequently has the white light emitted by that LED 8 passingtherethrough.

In addition, the LEDs 8 are powered electrically by an electrical powersupply unit 10 (represented diagrammatically in this example solely forone lighting outlet 5), arranged to power each LED 8 with different andvariable current levels depending on which one of the optical filters 12is positioned in front of the LED 8 to filter its light. The powersupply unit 10 may be in the form of a single power supply for all ofthe LEDs 8 of the lighting device 6, or it may be in the form of aplurality of power supplies respectively associated with each of theLEDs 8.

Advantageously, each time the disk 11 turns about the axis A in order toalign the LEDs 8 with one specific type of optical filter 12, the powersupply unit adjusts the currents passing through the LEDs 8 so as toconserve substantially constant light flux leaving the lighting device6, i.e. so as to conserve substantially constant visual illumination inthe lighting field, regardless of the type of filter that is placed infront of the LEDs 8. The term “substantially constant” is used to meanthat the light flux is identical to within 5% on each change of opticalfilter 12.

For each position of the disk 11 about the axis A, the four LEDs 8 arepreferably aligned with respective optical filters 12 of the same type,such that the lighting device 6 presents uniform light flux. For thispurpose, provision may be made for the spacing between two successiveLEDs 8, referenced E in FIG. 4, to be substantially equal to the spacingbetween two optical filters 12 of the same type forming parts of twosuccessive sets of filters.

The optical filters 12 are preferably specified in such a manner thatthe minimum and maximum color temperatures obtained after attenuatingthe blue peak lie in the range that is authorized by the standard IEC60601-2-41. In particular, the color temperatures that are commonlyencountered in operating theaters should be selected.

By way of particular example, the disk 11 carries a total of twelveoptical filters 12 arranged in four identical sets, each associated withone respective LED and each comprising three optical filters 12 of typesthat are different and progressive, thereby enabling three colortemperatures to be obtained that are different and progressive.

The term “progressive” is used to mean that the optical filters 12 areselected so as to establish a transmission difference between twosuccessive types of optical filter in a given set of optical filters 12,with this transmission difference preferably being at least 15%. By wayof example, within a set of three optical filters associated with a LED8, the first optical filter 12 thus has a first transmission coefficientthat does not modify the color temperature and that enables a maximumcolor temperature to be obtained, 5000 K in this example, the secondoptical filter 12 has a second transmission coefficient that enables anintermediate color temperature to be obtained, 4500 K in this example,and the third optical filter 12 has a third transmission coefficientthat enables a minimum color temperature to be obtained, 3900 K in thisexample.

FIG. 5 plots an example of the transmission coefficients 12A, 12B, and12C of the three progressive optical filters in a set of optical filters12 as a function of wavelength. FIG. 5 is given by way of example for anangle of incidence of the light on the filters of 30%. For some otherangle of incidence, the transmission coefficients vary a little as afunction of wavelength.

As can be seen in FIG. 5, the three optical filters 12A, 12B, and 12Care suitable for absorbing a red component of the light emitted by theLED 8 in order to reduce the radiant energy without modifying the colortemperature and without modifying the color rendering of the lightemitted by the LED 8. The drop in the radiant energy is of the order of0.4 milliwatts per square meter per lux (mW·m⁻²·lux⁻¹) to 0.5mW·m⁻²·lux⁻¹. In the example of FIG. 5, the transmission coefficients ofthree optical filters 12A, 12B, and 12C all present a threshold beyondwhich the transmission coefficient drops to reach 2% for wavelengthslonger than 740 nm. This threshold is referenced S in FIG. 5, and inthis example it is situated at a wavelength of about 700 nm, however itcould lie in the range 670 nm to 750 nm, and it should be adapted inparticular depending on the type of LED 8 used and on the angle ofincidence of the light emitted by the LED 8 onto the filter.

FIG. 5 also shows that the first optical filter has a transmissioncoefficient of 96%±2% for wavelengths shorter than 700 nm. This firstoptical filter 12A thus serves to conserve the color temperature of thelight emitted by the LED 8 while limiting the production of heat.

Finally, FIG. 5 shows that the second and third optical filters 12B and12C also attenuate the blue component of the white light emitted by theLED 8 and corresponding to the blue peak of the emission spectrum shownin FIG. 1, i.e. the wavelength around 450 nm, and preferably attenuatingblue components at wavelengths lying in the range about 400 nm to about480 nm.

More precisely, the second optical filter 12B has a transmissioncoefficient equal to 83%±2% for wavelengths lying in the range 400 nm to480 nm, and then a transmission coefficient that increases withincreasing wavelength from 83% up to 97%±2% for wavelengths lying in therange 480 nm to 620 nm. The third filter 12C has a transmissioncoefficient equal to 64%±2% for wavelengths lying in the range 400 nm to480 nm, and then a transmission coefficient that increases withincreasing wavelength form 64% up to 97%±2% for wavelengths lying in therange 480 nm to 620 nm. These second and third optical filters 12B and12C thus enable the color temperature of the light emitted by the LED 8to be modified, each of them reducing the color temperature by 600 K,while also limiting the production of heat. Thus, the optical filtermeans 12 enable the color temperature of the light emitted by the LED 8to be modified.

Depending on the application, the optical filters 12 may be made ofglass or of plastics material. The optical filters 12 are preferablyfabricated by depositing thin films under a vacuum or by a sol-geltechnique, onto a transparent substrate.

The disk 11 carrying the optical filters 12 may advantageously be turnedby a motor 13 controlled by a control unit 14 shown in FIG. 4, so thatthe surgeon can change the optical filters 12 simply and quickly byacting on the control unit 14.

The LEDs 8 of the lighting outlets 5 are preferably substantiallyidentical to one another so as to avoid any differences in light fluxand/or spectrum in the visible range from one lighting outlet 5 toanother. In particular, it is preferable for the LEDs 8 to be selectedso that they come from the same supplier, e.g. having the same type ofphosphorous-based component, the same package, the same electronic chip,and requiring the same type of power supply. White LEDs 8 should beselected that have a high color rendering index, lying in the range 85to 100, preferably lying in the range 90 to 100, or indeed in the range95 to 100, and a color temperature lying in the range 3000 K to 6700 Kin order to comply with the standards in force concerning lighting inmedical situations.

Naturally, the present invention is not limited to the above descriptionof a single embodiment thereof, and it may be subjected to variousmodifications without thereby going beyond the ambit of the invention.

For example, it is naturally possible to have some other number ofoptical filters 12 associated with each LED in the lighting device 6. Itis also possible to have some other number of LEDs 8 and of lightingoutlets 5 in the lighting device 6. Finally, some other number oflighting devices 6 may be provided in each overhead light 4. Thecross-shape for the light 4 is given purely by way of example.

By way of example, it is possible to use a LED that emits white light ata low color temperature, e.g. 3000 K. Under such circumstances, theoptical filters 12 should be selected so as to be capable of increasingthe color temperature of the light, e.g. by attenuating red componentsof the light in the range 600 nm to 700 nm.

Provision may also be made to use other types of optical filter, e.g.that attenuate ultraviolet components of the light.

What is claimed is:
 1. A lighting device, comprising: an LED configuredto emit white light; a collimator; a plurality of optical filters; and apower supply; wherein the plurality of optical filters is disposedbetween the collimator and the LED; wherein the plurality of opticalfilters are disposed on a support member, the support member configuredto rotate about an axis of the lighting device; wherein the plurality ofoptical filters includes a first optical filter and a second opticalfilter, the first and second optical filters having differenttransmission coefficients and being positionable to filter the whitelight emitted by the LED individually, so as to modify the colortemperature of the white light emitted by the LED; wherein the powersupply varies a power supply current supplied to the LED based onwhether the first optical filter or the second optical filter ispositioned to filter the white light emitted by the LED; wherein atleast one of the first and second optical filters attenuates a bluecomponent of the white light emitted by the LED at a wavelength lying inthe range 400 nm to 480 nm, a color rendering index of the white lightemitted by the LED staying in a range of 85 to 100; wherein thetransmission coefficient of the first optical filter and the secondoptical filter is one of 96%±2% for wavelengths shorter than 700 nm,83%±2% for wavelengths in the range of 400 nm to 480 nm, and 64%±2% forwavelengths in the range of 400 nm to 480 nm; and wherein thetransmission coefficient of the first optical filter and the secondoptical filter is 2% or less for a wavelength in the ramie of 730 nm to780 nm.
 2. The lighting device according to claim 1, wherein at leastone of the first and second optical filters is suitable for attenuatinga red component of the light emitted by the LED.
 3. The lighting deviceaccording to claim 2, wherein both of the first and second opticalfilters are suitable for attenuating a blue component of the lightemitted by the LED at a wavelength lying in the range 400 nm to 480 nm.4. The lighting device according to claim 3, wherein the first andsecond optical filters have progressive transmission coefficients forattenuating the blue component.
 5. The lighting device according toclaim 4, wherein the attenuation difference between the first and secondoptical filters is at least 15%.
 6. The lighting device according toclaim 1, wherein the first and second optical filters are arranged atthe periphery of the support member.
 7. The lighting device according toclaim 1, wherein the support member is a rotary disk.
 8. The lightingdevice according to claim 1, wherein at least one of the first andsecond optical filters is configured to attenuate red components of thewhite light in the range of 600 nm to 700 nm.
 9. A lighting device,comprising: an LED configured to emit white light; a collimator; aplurality of optical filters; and a power supply; wherein the pluralityof optical filters is disposed between the collimator and the LED;wherein the plurality of optical filters are disposed on a supportmember, the support member configured to rotate about an axis of thelighting device; wherein the plurality of optical filters includes afirst optical filter and a second optical filter, the first and secondoptical filters having different transmission coefficients and beingpositionable to filter the white light emitted by the LED individually,so as to modify the color temperature of the white light emitted by theLED; wherein the power supply varies a power supply current supplied tothe LED based on whether the first optical filter or the second opticalfilter is positioned to filter the white light emitted by the LED;wherein a quantity of light flux leaving the LED and lighting anilluminated field when the first optical filter is positioned to filterthe white light, and a quantity of light flux leaving the LED andlighting the illuminated field when the second optical filter ispositioned to filter the white light, remain substantially constantrelative to each other; wherein the transmission coefficient of thefirst optical filter and the second optical filter is one of 96%±2% forwavelengths shorter than 700 nm, 83%±2% for wavelengths in the range of400 nm to 480 nm, and 64%±2% for wavelengths in the range of 400 nm to480 nm; and wherein the transmission coefficient of the first opticalfilter and the second optical filter is 2% or less for a wavelength inthe range of 730 nm to 780 nm.
 10. The lighting device according toclaim 9, wherein the first and second optical filters arelight-attenuating optical filters that attenuate a blue component of thewhite light emitted by the LED.
 11. The lighting device according toclaim 9, wherein at least one of the first and second optical filters isconfigured to attenuate red components of the white light in the rangeof 600 nm to 700 nm.
 12. The lighting device according to claim 9,wherein the quantity of light flux leaving the LED and lighting theilluminated field when the first optical filter is positioned to filterthe white light, and the quantity of light flux leaving the LED andlighting the illuminated field when the second optical filter ispositioned to filter the white light, remain within 5% of each other.